// Copyright (c) 2006-2024, Timothy A. Davis, All Rights Reserved.
// SPDX-License-Identifier: LGPL-2.1+
// https://github.com/DrTimothyAldenDavis/SuiteSparse/tree/dev/CSparse/Source

/**
 * Keeps entries in the matrix when the callback function returns true, removes the entry otherwise
 *
 * @param {Matrix}   a              The sparse matrix
 * @param {function} callback       The callback function, function will be invoked with the following args:
 *                                    - The entry row
 *                                    - The entry column
 *                                    - The entry value
 *                                    - The state parameter
 * @param {any}      other          The state
 *
 * @return                          The number of nonzero elements in the matrix
 */
export function csFkeep(a, callback, other) {
  // a arrays
  var avalues = a._values;
  var aindex = a._index;
  var aptr = a._ptr;
  var asize = a._size;
  // columns
  var n = asize[1];
  // nonzero items
  var nz = 0;
  // loop columns
  for (var j = 0; j < n; j++) {
    // get current location of col j
    var p = aptr[j];
    // record new location of col j
    aptr[j] = nz;
    for (; p < aptr[j + 1]; p++) {
      // check we need to keep this item
      if (callback(aindex[p], j, avalues ? avalues[p] : 1, other)) {
        // keep A(i,j)
        aindex[nz] = aindex[p];
        // check we need to process values (pattern only)
        if (avalues) {
          avalues[nz] = avalues[p];
        }
        // increment nonzero items
        nz++;
      }
    }
  }
  // finalize A
  aptr[n] = nz;
  // trim arrays
  aindex.splice(nz, aindex.length - nz);
  // check we need to process values (pattern only)
  if (avalues) {
    avalues.splice(nz, avalues.length - nz);
  }
  // return number of nonzero items
  return nz;
}